Optical waveguide and process for manufacturing the same

Abstract

The present invention provides an optical waveguide, which at least includes: a waveguide core having a cavity therein; and a clad which encloses the periphery of the waveguide core and has a smaller refractive index than the waveguide core, wherein the optical waveguide changes a direction of a part or all of propagated light by using a part or all of an interface between the waveguide core and the cavity as a reflecting surface. The present invention further provides a method for manufacturing the optical waveguide, which at least includes: forming a core having a cavity therein on a substrate; applying an uncured clad material to a side surface and an upper portion of the core while maintaining the cavity which allows an atmospheric gas to be present in the cavity; and curing the clad material by heat or light to seal the gas in the cavity.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims priority under 35USC 119 from Japanese Patent Application No. 2005-162705, the disclosure of which is incorporated by reference herein.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to an optical waveguide having the function of changing the direction of light propagation.[0004]2. Description of the Related Art[0005]Since the technology of high-speed transmission of signals using electricity is approaching its limit, there are great expectations in the role of optical transmission. In this situation, the realization of an opto-electric hybrid board is regarded as a today's urgent task. In order to realize the opto-electric hybrid board, an optical waveguide corresponding to a highly integrated electrical device is required. It is required for the optical waveguide to attain a large change in the direction of light propagation in a small space within limits imposed by th...

AI Technical Summary

Benefits of technology

The present invention provides an optical waveguide that can change the direction of light propagation by using a reflecting surface created by a cavity within the waveguide core. This allows for more efficient light coupling and can be done at a low cost with ease of manufacture. The reflecting surface can be designed to have a specific reflecting angle and width, and can be optionally branched to form a Y-shaped waveguide with reduced excess loss. The invention also provides a method for manufacturing the optical waveguide and a design for the reflecting surface that improves reflection efficiency and reduces excess loss.

Problems solved by technology

Although methods of changing the direction of light propagation using various polymer waveguides are being considered, there are problems such as those described in the following (1) to (3) are imposed.

However, it is not possible to avoid a loss caused by utilization of a radiation mode when an arc is used.

However, since the difference in refractive index between a core and a clad is small, a large change in direction was not possible.

Also, complete total reflection cannot be performed and there is a leakage of light at the total reflecting surface.

However, it is impossible to carry out cutting locally.

Also, because the polymer optical waveguide is actually cut in this cutting process, it is difficult to attain this cutting at a place except for the end surface of the optical waveguide.

Also, because accuracy of the dicing position is required, leading to an increase in the number of steps as well bringing about high costs.

By this method, the reduction in leakage of light reduces the optical loss and the curvature radius can be made small; however, a limitation to miniaturization remains as before.

However, in this method, since the air clad layer is located on the exterior, the manufacturing process is complicated and the air clad cannot be easily produced.

In the configuration disclosed in JP-A No. 2003-75670, the air clad is formed by etching, but the surface formed by etching tends to be rough, giving rise to the problem that the reflecting surface has a degraded reflecting efficiency.

Further, the equipment cost for etching tends to be higher, and the etching process itself is disadvantageous timewise.

Also, because the void is an air cell, the whole end surface of the waveguide is not completely in contact with the void due to the method of depositing clad materials and the planar interface is not a perfectly flat surface, optical loss caused by these reasons is inevitable.

Also, the configurations in JP-A Nos. 11-248951 and 2003-75670 must have the whole core of the optical waveguide as a total reflecting surface, and it is therefore impossible to make a branched waveguide structure.

Also, in widely used methods in which a Y-branch or the like is used in a branched waveguide to divide light into plural branches, an increase in a branched angle is accompanied by an increase in light leakage and it is therefore impossible to branch light at a wide angle.

The fundamental cause of these problems is a limitation in the refractive indices of the core and the clad to be used because the NA becomes defined under the conditions of connections between the optical parts such as a fiber and the like and the optical waveguide.

Also, when a polymer having a degree of freedom is used in designing a waveguide, the refractive index of the polymer used for the clad is limited.

Therefore, when designing a waveguide without considering NA, such as in the case of directly connecting the waveguide with an optical transmitting and receiving device, the clad is not allowed to have a refractive index significantly different from that of the core, with the result that the direction of light propagation cannot be significantly changed.

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